snoopy: add ipmux pseudo protocol

the ipmux pseudo protocol handles the extra ipv6 interface address
prefixed to the ip header as used by /net/ipmux packet filter.

sys/src/cmd/ip/snoopy/ipmux.c

@@ -0,0 +1,103 @@
+#include <u.h>
+#include <libc.h>
+#include <ip.h>
+#include "dat.h"
+#include "protos.h"
+
+typedef struct Hdr Hdr;
+struct Hdr {
+	uchar	ia[16];
+	uchar	data[1];
+};
+
+static Mux p_mux[] =
+{
+	{"ip",		0x40, },
+	{"ip6", 	0x60, },
+	{0}
+};
+
+enum
+{
+	Oia,	/* interface address */
+	Ot,	/* ip type */
+};
+
+static Field p_fields[] =
+{
+	{"ia",	Fv6ip,	Oia,	"interface address", },
+	{"t",	Fnum,	Ot,	"ip type" },
+	{0}
+};
+
+static void
+p_compile(Filter *f)
+{
+	Mux *m;
+
+	if(f->op == '='){
+		compile_cmp(ipmux.name, f, p_fields);
+		return;
+	}
+	for(m = p_mux; m->name != nil; m++)
+		if(strcmp(f->s, m->name) == 0){
+			f->pr = m->pr;
+			f->ulv = m->val;
+			f->subop = Ot;
+			return;
+		}
+	sysfatal("unknown ipmux field or protocol: %s", f->s);
+}
+
+static int
+p_filter(Filter *f, Msg *m)
+{
+	Hdr *h;
+
+	if(m->pe - m->ps <= 16)
+		return 0;
+
+	h = (Hdr*)m->ps;
+	m->ps += 16;
+
+	switch(f->subop){
+	case Oia:
+		return memcmp(h->ia, f->a, 16) == 0;
+	case Ot:
+		return (h->data[0]&0xF0) == f->ulv;
+	}
+	return 0;
+}
+
+static int
+p_seprint(Msg *m)
+{
+	int len;
+	uint t;
+	Hdr *h;
+
+	len = m->pe - m->ps;
+	if(len <= 16)
+		return -1;
+
+	h = (Hdr*)m->ps;
+	m->ps += 16;
+
+	t = h->data[0]&0xF0;
+	demux(p_mux, t, t, m, &dump);
+
+	m->p = seprint(m->p, m->e, "ia=%I t=%2.2ux ln=%d", h->ia, t, len);
+	return 0;
+}
+
+Proto ipmux =
+{
+	"ipmux",
+	p_compile,
+	p_filter,
+	p_seprint,
+	p_mux,
+	"%#.2lux",
+	p_fields,
+	defaultframer
+};

sys/src/cmd/ip/snoopy/mkfile

@@ -19,6 +19,7 @@ PROTOS=\
 	eapol\
 	eapol_key\
 	ether\
+	ipmux\
 	gre\
 	hdlc\
 	icmp6\